The invention relates generally to EMI filtering and more particularly to a method of combining optical waveguides with standard circuit board elements to create an electro-magnetic interference (EMI) shield with a means for transmitting signals through the shield barrier optically.
Circuit board assemblies often contain circuits that are susceptible to EMI, such as microprocessors, in close proximity to EMI generating circuits, such as microwave amplifiers, or circuits corrupted by EMI from external sources, such as power switches connected to external loads. These problems have generally been addressed by constraining the location of the susceptible circuits on the circuit board(s) to areas far removed from the EMI generating circuits or wires. These problems have also been addressed by shielding the susceptible circuits and using filtered connections for signaling from these circuits. Yet another technique that has been employed is placement of the susceptible circuits entirely on a separate card assembly. Although the foregoing techniques each provide corresponding advantages, each of these techniques significantly constrains the associated circuit design and may not provide entirely effective shielding of the susceptible circuits from interference. A challenge not yet met by known techniques is the need for shielding susceptible circuits to high frequency EMI (up to about 40 GHz) while providing a means for signaling between the susceptible circuits and external devices.
In view of the above, it would be both advantageous and beneficial to provide an effective high frequency EMI shield for standard circuit board assemblies/elements that allows signals generated via the standard circuit board assemblies/elements to effectively pass through the EMI shield barrier while shielding high frequency EMI.